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Condensation, Evaporation, and Boiling
Published in Anthony F. Mills, Heat and Mass Transfer, 2018
Forced-flow boiling and condensation in horizontal or vertical tubes and channels occurs in such diverse equipment as water-tube boilers, refrigerator evaporators and condensers, water-cooled nuclear reactors, and a great variety of process and chemical equipment. In a water-tube boiler, addition of heat changes the water flow to a two-phase flow of water and vapor, and finally to a pure vapor flow; in a tube condenser, the reverse process occurs. In each case, the two-phase flow is very complex, and many distinct flow patterns can be identified, such as bubbly flow, slug flow, and annular flow. Just predicting the flow pattern for specified system parameters is a difficult task. Reliable prediction of pressure drop and heat transfer is even more difficult, owing to the complexity of the flow patterns.
Introduction
Published in L. S. Tong, Y. S. Tang, Boiling Heat Transfer and Two-Phase Flow, 2018
Two-phase flows are classified by the void (bubble) distributions. Basic modes of void distribution are bubbles suspended in the liquid stream; liquid droplets suspended in the vapor stream; and liquid and vapor existing intermittently. The typical combinations of these modes as they develop in flow channels are called flow patterns. The various flow patterns exert different effects on the hydrodynamic conditions near the heated wall; thus they produce different frictional pressure drops and different modes of heat transfer and boiling crises. Significant progress has been made in determining flow-pattern transition and modeling.
Review of Single-Phase Flow
Published in Clement Kleinstreuer, Theory and Applications, 2017
A sound understanding of the physics of single-phase flow and a mastery of solution techniques for single-phase flow problems are important prerequisites for studying two-phase or multiphase flow systems. Two-phase flow is best described as the flow of two different kinds of matter, e.g., solid particles in a gas or liquid, gas bubbles in a liquid, or droplets in a gas stream. As always, the objective is to learn to develop mathematical models, here, approximate representations of actual two-phase flow phenomena in terms of differential or integral equations. The (numerical) solutions to the describing equations should produce testable predictions and allow for the analysis of two-phase system variations leading to a deeper understanding and possibly to new or improved system designs.
Instability of Low-Velocity and High Water-Cut Oil–Water Two-Phase Flow Based on Microwave Signals
Published in Heat Transfer Engineering, 2023
Landi Bai, Jing Ma, Weixin Liu, Ningde Jin
Two-phase flow widely exists in the field of chemical industry, aerospace, environment protection, petroleum exploitation, and so on. The study of oil–water two-phase flow is very important in petroleum exploitation. However due to long-term water flooding, the production characteristics of low permeability and low yield are particularly significant. Accurate measurement of the flow characteristics of oil–water two-phase flow in the wellbore is crucial to the understanding of reservoir production characteristics [1, 2]. However, due to the significant slippage of the low-velocity and high water-cut oil–water two-phase flow, the local concentration and velocity distribution of the dispersed phase are not uniform, and complex droplet coalescence and crushing phenomenon occur with the change of flow parameters [3]. Understanding the dynamic of flow patterns is crucial to important problems such as predicting the pressure drop and flow measurement [4, 5].
Aeroelastic flutter analysis of tilted curved nanopipe in supersonic flow
Published in Mechanics of Advanced Materials and Structures, 2023
Ke Wu, Gang Wang, Xin Li, Yasuo Liu
Two-phase flows are usually characterized by the volume fractions of their components. In this regard, based on the amount of the gas or liquid in the flow, the following categories are recognized in the two-phase gas-liquid flows: The first category is composed mostly of the liquid phase and the gas phase appears in the form of bubbles and is hence called bubbly flow.the second category contains more gas phase and larger bubbles appear in the flow and it is called slug flow.If the amount of gas volume fraction increases so that very large and unstable bubbles appear in the flow and cause the flow to be turbulent and unstable, the third category called Chunn flow manifests.The fourth category is mostly the gas phase and the liquid is pushed to side boundaries of the flow. This type is called annular flow.
Effects of Mixing Vane Spacer on Flow and Thermal Behavior of Fluid in Fuel Channels of Nuclear Reactors—A Review
Published in Nuclear Technology, 2020
Satish Kumar Dhurandhar, S. L. Sinha, Shashi Kant Verma
Nowadays, many systems based on two-phase flow extensively come up in several industrial fields, such as nuclear, chemical, and petrochemical engineering. Tubes, annular channels, and rod bundles are common fluid flow domains used in various industries, such as chemical plants, steam generators, heat exchangers, nuclear reactor cores, etc. Hence, for the safe operation of nuclear reactors and the optimum design of nuclear fuel rod bundles with mixing vane spacer grids, the investigation of two-phase flow characteristics has a useful and essential role in nuclear fuel rod bundles. However, in nuclear fuel rod bundles the flow characteristics of two-phase fluid are very complex due to robust secondary flow between subchannels, relative motion in fluids of two-phase flow, complicated flow patterns, and the occurrence of interface distortion. The accurate prediction of thermal and hydraulic performance of two-phase flows in the fuel rod bundles of nuclear reactors depends on the proper analysis of spacer grid mixing vane effects on flow characteristics, phase interaction mechanisms [analysis of interfacial area concentration (IAC)], and flow characteristic distribution of two-phase fluids (analysis of void fraction distribution, bubble size distribution, and bubble velocity distribution).